In the context of the MPEG-7 standard, description of multimedia data consists of descriptors (Ds) and description schemes (DSs), where the number of description elements (Ds or DSs) can be variable. (Reference is herein made to ISO/IEC, “Introduction to MPEG-7”, Doc. ISO/IEC JTC1/SC29/WG11 N3751, La Baule, France, October 2000). All Ds and DSs in MPEG-7 are defined using the so-called Description Definition Language (DDL). (Reference is herein made to ISO/EEC, “Text of ISO/IEC CD 15938-2 Information technology—Multimedia content description interface: Description Definition Language”, Doc. ISO/IEC JTC1/SC29/WG11 N3702, La Baule, France, October 2000). Further, an MPEG-7 description can be represented either in textual format (XML) or in binary format (BiM). In order to allow interoperability between applications using MPEG-7, the set of Ds and DSs comprised in MPEG-7 needs to be fixed at a certain point in time. While the DDL 25 then still allows to extend MPEG-7 DSs, going beyond the predefined set, the meaning of these new (extended) DSs will not be known to anybody but the one who designed it.